Is there a way to manipulate objects as group in Blender 2.8?
A collection allows to create collection instances.



As p2or said in comments, you can also in 3D view ShiftA, then 'collection instance' and choose the collection you want to instanciate.

Once done, you use the instance as one object:

On the right here the original collection, on the left, the instance that you can manipulate as if it is an object:



You can "edit" the instance from its base collection:

Either manipulating the individual objects:



Or modifying them in edit mode: